graduation tower
A wall-like or tower-like framework built to hold a mesh for the production of salt or salt spray.
A graduation tower concentrates brine by letting it trickle over bundles of brushwood, usually blackthorn, held in a tall wooden frame. Part of the water evaporates on the way down and the minerals settle on the twigs, which are renewed every five to ten years.
The towers were built for salt production and stand mostly in Germany, Poland and Austria. The German term is Gradierwerk. Most of the surviving examples belong to spa towns, where the salt-laden air is offered as a treatment.
The brushwood presents a large exposed surface over which the brine can spread and evaporate. The supporting frame holds this working surface; a tall enclosed tank for storing brine has a different form.
graduation tower Photos
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